The terrestrial biosphere currently absorbs about a quarter of the anthropogenic carbon emissions. Can this carbon sink help to mitigate climate change? In their Perspective, the authors argue that the world will not be worse off for having undertaken measures to promote land sinks, provided that steps to reduce emissions from fossil fuel combustion are not compromised and deforestation is avoided. Even if used to the maximum, however, these sinks will make only a minor difference to the final concentration at which atmospheric CO2 stabilizes. Emphasis must therefore be placed on reducing fossil fuel use and avoiding deforestation.